Method of making filaments for miniature incandescent lamps and articles



Jan. 12,1937. W HENR 2,067,664

METHOD OF MAKING FILAMENTS FOR MINIATURE INCANDESCENT LAMPS AND ARTICLES Filed June 27, 1932 i a A? 23 INVENTOR WILL/AM JT HEN?! ATTORNEYS Patented Jan. 12, 1937 UNITED STATES PATENT OFFICE METHOD OF MAKING FILAMENTS FOR IVHNIATURE INCANDESCENT LAMPS AND ARTICLE S 1 Claim.

This invention relates to incandescent lamps and procedure and apparatus for making the same.

It has heretofore been desirable to produce a small, round source of illumination for use in optical instruments such as a retinoscope (or skiascope), but so far such light source has not been obtainable. It has also been proposed heretofore to provide incandescent lamps for various uses in which a double. helical filament coil is employed. These incandescent lamps, however, have not been satisfactory because of shorting due to touching of adjacent coils of the double helix.

It has been found by the present inventor that a double helical coil may be efiectively provided for use in optical instruments to provide a small, perfectly round light source which will be very effective in the determination of defects in the eye by the use of such instruments as the retinoscope if the diameter of the .double helical coil as compared with the size of the filament is such that the double helical coil will be stiff enough so that it cannot be distorted or shorted by the ordinary jars or shocks to which these bulbs are subjected in service and if the double helical coil is made by the method disclosed herein to prevent touching of the adjacent convolutions of the coils in service.

The present inventor has discovered that the natural expansion of the filament wire under heat results, in a double helical coil, in the distortion which causes movement of the adjacent coils with respect to each other, which movement has hereto-fore caused shorting, and that by winding the coils as disclosed herein with an uneven spacing and preheating the coils whereby this distortion is caused to relatively move the coils to more or less equal spacing, the danger of shorting by touching of the coils is eliminated, any movement which occurs in the coils when subsequently used tending, if anything, to move the coils farther apart.

The double helical coil in an optical instrument is especially effective since in a comparatively short filament of small diameter the leads or mounting wires absorb so much of the heat as to prevent the ends of the filament from heating to the extent of the .middle. The outer end, therefore, of the double helical coil gives the greatest amount of light, and when an incandescent bulb of this construction is mounted so that the source of light from the lamp in effeet is the outer end of the coil, a perfectly round and true light source of small diameter is provided.

The present invention, accordingly, has for its general purpose the provision of an incandescent lamp having an improved double helical coil construction and the provision of an improved method and improved apparatus for making such an incandescent lamp.

The invention is illustrated in the accompanying drawing and described in somewhat more detail below. It is to be understood that the invention is not limited to the specific form thereof illustrated and described.

Of the accompanying drawing,

Figure 1 is an elevation, partly in section, a coil winding equipment embodying the invention;

Figure 2 is an enlarged plan view thereof;

Figure 3 is a view similar to Figure 2 show ing the coil as wound therein and illustrating the manner of attaching the leads to the coil;

Figure 4 is a right end view of Figure 3;

Figure 5 is an elevation of an incandescent lamp embodying the invention; and

Figure 5*- is an enlarged view of the improved filament as shown in Figure 5.

Referring to the drawing, the numeral l0 designates a coil winding mandrel which is secured on a rotatable shaft H which may be mounted in bearings l2, l2 on a suitable support I3, the shaft ll having an off-set portion l I adjacent the mandrel for a purpose which will be described. The shaft ll may have a knurled end Ii thereon in which a threaded bore l I is provided to receive a threaded shaft M which is adjustably secured in a clamp at I5 which may be actuated by a knurl wheel l5 either to permit the shaft M to be slid through the clamp l5 or to secure the shaft l4 when desired. Associated with the mandrel H] are filament supports I1 and IS, the support I! having a shoulder ll over which the filament extends and the support l8 having a hook l8 under which the filament extends to support a straight portion of the filament as indicated at 19 between the supports I1 and I8 in proper relation to be engaged by the mandrel ID to wind the coil. The supports I! and 18 may be arranged on a plate 20 secured in any suitable way on support l3. Grooved guides 2| and 22 are also provided for supporting and guiding the filament to the mandrel I0 and are arranged in such relation with respect to the supports I! and I8 that the filament extends at angles to the straight portion l9 as indicated at I9 and I9 The filament in the various views is generally indicated by the letter F. The mandrel II) has a filament engaging groove in the end thereof as indicated at Ill the ends of the mandrel at each side of the groove being curved as indicated at lll HI so that when the filament wire is formed into a double helix the coils adjacent the outer end of the double helix will lie smoothly in true circle shape against the mandrel. J

To wind a filament coil by the apparatus as described above, the clamp I5 is released and shaft II is slid forwardly in its bearings l2 to engage the groove Ill of mandrel H] with the straight portion I9 of the. filament as shown in Figure 2. The shaft I4 is then clamped in clamp I 5 so that it may not move and shaft I I is turned which causes the shaft II to feed forwardly at a rate determined by the pitch of the screw threads-x on shaft l4 and in the bore ll. This pitch is,.of, g

' rod M, giving a finished coil .0273" in length,

course, the desired pitch of the double helical coil to beformed.

It will be noted that supports l1 and IE1 are so arranged with respectto the end of the mandrel that as the filament is wound into the'double helical coil as indicated in Figure 3, the windings of the respective coils of the double helix are spaced so as to lie comparatively'close together in pairs with a comparatively large spacing between the pairs of coils whichis determined by the pitch of the screw on rod or shaft I4. The first half of the filament, as will be noted, passes under the hook I8 and over the mandrel as shown in Fig-' ure 3, whereas the outer half of the filament passes over the shoulder lie and under the mandrel, the support l8 being arranged to guide the filament to the mandrel from a point farther inwardly of the outer end of the mandrel than the support l1. As stated above, with this type of winding, the filament when heat-treated in the finished bulb expands in such a way under the action of the heat that the adjacent coils of the double helix move apart from the position shown in Figure 3 to the position shown in Figure 5 The stretches of the filament over the guides 2| and 22 may be connected with suitable means for maintaining the filament under tension so that ment. After the filament is secured to the leads it will assume the position thereof shown in Figure 2 preliminarily to winding and so that it will wind snug and true about the mandrel l during the winding operation.

After the filament has been Wound as shown in Figure 3, the leads and mount for the filament comprising leads L, L and bead B indicated in dash and dot lines are positioned as shown. Suitable yielding clamps 23, 23 arranged to cooperate with platforms 24, 24 and normally urged downwardly by springs such as spring 25 are provided to clamp the leads L, L as indicated in Figure 3 with the bead B positioned in the space provided by the offset I l in the shaft H whereby the usual hook ends of the leads L, L may be engaged about the portions I9 and [9 of the filament F and clamped thereon by suitable means (not shown). By reason of the fact that the portions W and l9 extend at an angle, the filament is thus clamped to the leads so that it will be supported in proper position axially of the lamp bulb and cannot rock out of position, the angularity of the clamp filament preventing any tendency of the clamped portions of the filament to rotate about their axes. It will be understood that the hooked ends of the leads are squeezed to compress the hooks about the angular stretches of the filawhen the incandescent lamp made as described herein is mounted so that the outer end of the coil provides the light source,this source will be perfectly round.

As stated in a preceding paragraph, the diam eter of the coil must be sufiiciently small that "the resulting coil will be sufliciently stiff to prevent distortion by such jarring as ordinarily occursin service, It. has been found that with a mandrel .00875"'in diameter, the usual filament wire used in miniature lamps, when wound into a double helical coil is sufiiciently stifi to resist distortion by .jarring. A suitable coil is provided of this size using 128 threads to the inch on the having 3 turns; and when tempered or set as described having a; finished diameter of .01125". It is understood of course that these dimensions are merely demonstrative and maybe varied.

After the filament has been mounted in the lamp 'asshownin Figure 5, it is given a pre-treatmentwith heat by attaching the bulb in the usual socket and witha rheostat or other suitable electricallyv controlled device gradually increasingthe current and voltage supplied to the lamp until its-operatingcurrent and voltage is reached. This causes the closely spaced adjacent coils of the double helix to move apart so that the coils of the filament in the finished lamp are substantially equally spaced as indicated in Figure 5 Thereafter, whether the .current is supplied gradually or suddenly to the lamp in service to its rated current and voltage, the coilsdo not move together and touch one another to cause shorting, a difiiculty which has heretofore been experienced in this type of coil. As a matter of fact, in the setting of the filament in its final form by the pre-heat treatment described, the coils may not move entirely .toequally spaced positions such as shown in Figure 5*, but in any event is subsequent use any. tendency for the coils to move under the action of heat will tend to separate them further rather than to bring them closer together. Regardless of whether they move to final equally spaced positions or notwhen heat treated, the movement of the coils in any condition of service cannot be of an amount sufilcient to cause touching and shorting.

Modifications of the invention may be resorted to without departing from the spirit thereof or the scope of the appended claim.

What is claimed is:

The method of making-a filament for incandescent lamps for use in diagnostic instruments and the like whichcompr'ises'winding a single length of wire into a helix and then winding reversely a return helix of the same size with the convolutions of each helix extending in parallel relation throughout the greater portion thereof and witha given convolution of one helix axially ar- WILLIAM J. HENRY. 

